450Bushmaster.net

Now that I am reloading and have a chrono, I would be interested in knowing what kind of data I should be collecting, when I try out my reloads. For example, I already collect chrono data including:

individual
average
median and
average velocities
standard deviation

In addition, I know my:

bullet type
powder brand and weight
primer
COL
crimp type and diameter

I also collect environmental data:

temperature
humidity
wind force and direction
altitude

.

Is there anything else?

Also, how many rounds should I shoot per group - 3, 5, or some other number? How should group size be measured - center to center of the two farthest apart shots or outer edge to outer edge?

IMHO, don't collect data you will not use to dictate your shooting or reloading after it is collected. IE Humidity is a factor, but I've never not gone shooting because of it, nor changed my load because I knew I would be shooting under extreme humidity conditions, either high or low. Ditto on altitude. Temperature is a factor with the ball powders we use in the 450B, but mainly come into play again, under extreme circumstances. IE developed when it was real cold and shot when it is real hot. SD while useful, is probably not as immediately useful as Extreme Spread from a visualization point of view.

As for number of shots. When I'm doing an initial search for a particular velocity or maximum safe velocity, a three shot group usually produces at least two velocities close to enough to one another to be credible data. When shooting to determine accuracy, IMHO three shots are not conclusive. In that case, five would be a minimum and if across several loads at the same time, shoot them round robin to avoid hot streaks. Five will definitely give you a useful result. With this caliber and in this platform, as opposed to a bolt action, you may have flyers that are not the fault of the load. Know them when you see them. Of course, practice will reduce the need.

Hoot

Round robin? Does that mean fire one round from each load consecutively? Sorry still trying to learn

gtoboi65 wrote:Round robin? Does that mean fire one round from each load consecutively? Sorry still trying to learn

Yes.

I use 4-up and 5-up targets, so I'm shifting the rifle around as little as possible. Their more busy than 1-up targets and hence a little more distracting, but I get used to that eventually. It tends to make the session go more slowly and given my impatience, that's actually a good thing. I still use a 1-up to sight in for obvious reasons.

Hoot

Think you. Yes I could imagine that the extra clutter would cause distractions to the eye. I'll have to give it a try!

I've been meaning to try the round robin method. I do worry that I would forget the sequence. My data pretty much mirrors Hoot except for the round robin bit. String # of shots, FPS, avg, ES, SD, temp, humidity, and detail load information and case expansion/shrink.

I also like before and after case expansion numbers. Those numbers, with speeds, can indicate powder amount changes or a powder brand switch..

..t

How do you measure case expansion and what is a round robin?

Jim in Houston wrote:How do you measure case expansion and what is a round robin?

You'll see a change in reflectivity in the case wall above the extraction groove. That's where expansion is occurring. Measure it with a micrometer. Not many calipers are accurate enough.

In this picture, you see four numbered targets with four different loads shot, one in each numbered target:



Round Robin involves loading one of each load sequentially and shooting one at each of the four targets. Repeat using the same sequence until done. If you turn out a good group, chances are it was not just a good 5 sequential shot string where you were doing everything right. If performance changes as the rifle heats up, that change is reflected in every load's group. If you have a good run, it will be reflected in every load's group.

Of particular interest is the fact that the target above was the same bullet, the same powder charge, the same COL, the same everything, except primers. Primer choice does matter! And yes, there are 5 shots in #3. It's a new, out of the box RRA LAR-8 Predator HP in .308, after 20 shoot one clean one break in shots. RRA makes good, off the shelf rifles.

It's no bull barrel, weight lifter's delight either. SS 20" Hbar barrel. Full A2 stock and only 8 lbs empty, without scope. My 450b, with all the recoil abatement stuff on it weighs more.

Hoot

OK, understand that you are dealing with an (or another?) engineer here. If I have one reloaded cartridge, say an FTX 250 with the powder, primer, etc., all the same, then I understand that I would shoot one round on each of the four targets in sequence, then repeat until I have 5 rounds on each target. That seems clear.

If I have reloaded two rounds, say an FTX 225 and an FTX 250, everything else is the same, then would I shoot one of the 250's on target #1, then one of the 225's on #2, 250 on #3, 225 on #4, then repeat until I have five rounds on each target? Each target would have the same rounds shot at it - 250's on #'s 1 and 3; 225's on #'s 2 and 4. Is that correct?

What if I have an odd number or different rounds, say 250's and 225's with different crimps? If I do a round robin, I could end up with mixed rounds on the same target - #1 could have a couple of 250's with a taper crimp, a 225 with a roll crimp (this is just an example), a 225 with a taper crimp and a 250 with a roll crimp, #2 could have different mix, etc. Or do I want to keep all of the same loads on each target, but just shoot them in sequence?

This could be a dumb question .